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Oracle Tips by Burleson |
Disk I/O Tuning
Chapter 3:
SCSI Tuning Under AIX
For
non-IBM devices, it is sometimes required to modify AIX default
queue-limit values to ensure highest performance rather than use
those that have been chosen to handle the worst possible case.
Let's look at situations in which the defaults should be changed
and the IBM recommended new values.
The
default settings for AIX for IBM disk drives for the number of
requests that can be outstanding at any given time is 3 (8 for SSA).
This value has no direct interface for changing it. The default
hardware queue depth for non-IBM disk drives is a very performance
killing 1. It behooves you to change the setting for Non-IBM drives
if they can accept multiple commands (most modern drives can), so
you can get the maximum performance from those drives. For example,
you can display the default characteristics of a non-IBM disk drive
with the lsattr command:
# lsattr -D
-c disk -s scsi -t osdisk
pvid
none Physical volume identifier False
clr_q no Device CLEARS its Queue on error
q_err yes Use QERR bit
q_type simple Queuing TYPE
queue_depth 3 Queue DEPTH
reassign_to 120 REASSIGN time out value
rw_timeout 30 READ/WRITE time out value
start_timeout 60 START unit time out value
You should use the AIX
provided interface, SMIT to change the disk parameters as
required. SMIT allows for
The above text is
an excerpt from:
Oracle Disk I/O Tuning
Disk IO Performance & Optimization for Oracle
Databases
ISBN
0-9745993-4-4
by Mike Ault
Oracle Consulting
Services
Burleson
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